This invention is generally directed to processes for the preparation of polycarbonates, inclusive of those obtained from bisphenols such as gem-bis(hydroxyaryl)alkanes, reference U.S. Ser. No. 067,588, now U.S. Pat. No. 4,766,255, entitled Processes for Bisphenols, the disclosure of which is totally incorporated herein by reference. More specifically, the present invention relates to processes for the purification of polycarbonates, especially polycarbonate (A), polycarbonates (Z), copolymers thereof, and the like, wherein undersirable impurities such as catalysts selected for the preparation thereof are removed. In one embodiment of the present invention there is provided a process for the purification of polycarbonates obtained from, for example, the known melt polyesterification reactions, which process comprises the formation of a complex with a titanium catalyst, and the removal thereof enabling polycarbonates with improved characteristics. Accordingly, with the process of the present invention there are obtained polycarbonates substantially free of titanium butoxide catalysts, which catalysts are selected in some instances for the preparation of polycarbonates. The purified polycarbonates obtained with the process of the present invention possess improved characteristics, including low dark decay values, and minimum residual potential with cycle up when these polycarbonates are selected as binders for transport molecules in layered imaging members as illustrated, for example, in U.S. Pat. No. 4,265,990, the disclosure of which is totally incorporated herein by reference. Also, with the purified polycarbonates of the present invention the undersirable crystallization of aryl amine molecules, which are dispersed therein for the formation of the aforementioned imaging members, is eliminated. Additionally, the toxic chemical phosgene is avoided with the process of the present invention. Also, with the process of the present invention there can be obtained purified polycarbonates of a weight average molecular weight of from about 25,000 to about 100,000, and preferably from about 26,000 to about 55,000. These molecular weights result, it is believed, since the more active catalysts comprised of titanium or zirconium alkoxides are initially selected for the preparation of the polycarbonate, which is then purified in accordance with the process of the present invention. When less active manganese acetate is selected for the preparation of polycarbonates, the weight average molecular weight of the polycarbonates obtained is lower, that is less than about 20,000 and about 16,000. The higher molecular weight polycarbonates of about 25,000 to about 100,000 possess increased toughness, and provide for a longer lasting and more resilient device when employed as the resin binder in layered imaging members.
Processes for the preparation of bisphenols are known, and generally involve the condensation of two mole equivalents of phenol with one mole equivalent of carbonyl compound in the presence of an acid catalyst. Acid catalysts employed for the aforementioned condensation are concentrated hydrochloric acid, gaseous hydrogen chloride, concentrated sulfuric acid, hydrogen fluoride, hydrogen bromide, boron trifluoride, boric acid, ferric chloride, phosphorus chloride, phosphorus pentoxide, benzenesulfonic acid, and the like. Although these acid catalysts, in particular gaseous hydrogen chloride, are very effective in promoting the condensation of phenols with sterically accessible ketones such as acetone, they are not effective for the preparation of bisphenols, especially bisphenol (Z) derived from the sterically demanding small cyclic ketone such as cyclopentanone or cyclohexanone. The condensation with small ring ketones does not normally proceed in a rapid manner, and the yield of product is generally less than desirable. The aforementioned reaction, especially when accomplished in the presence of hydrogen chloride as a catalyst, is illustrated in U.S. Pat. No. 4,304,899. Similar teachings are presented in U.S. Pats. No. 1,760,758; 2,069,560 and 2,069,573, wherein there are disclosed methods for the preparation of bisphenols with hydrogen chloride catalysts. The polycarbonates resulting from these bisphenols can be selected as resinuous binders for aryl amine hole transport compounds.